crack.c

#include <cs50.h>
#include <stdio.h>
#include <crypt.h>
#include <string.h>

int A_charcode = 65;
int a_charcode = 97;
int abc_size = 25;
string hash;
bool success = false;
int iterator = 0;

/**
 * replaces letter with the next one from alphabet
 * incrementLetter('a') => 'b'
 */
char incrementLetter(char letter) 
{
    return (char)((int)letter + 1);
}


#define ARRAY_CONCAT(TYPE, A, An, B, Bn) \
(TYPE *)array_concat((const void *)(A), (An), (const void *)(B), (Bn), sizeof(TYPE));

/**
 * concats 2 arrays
 * ARRAY_CONCAT("abc", "def") => "abcdef"
 */
void *array_concat(const void *a, size_t an,
                   const void *b, size_t bn, size_t s)
{
    char *p = malloc(s * (an + bn));
    memcpy(p, a, an * s);
    memcpy(p + an * s, b, bn * s);
    return p;
}

/**
 * slices array from start to end
 * slice("abc", 0, 2) => "ab"
 */
void *slice(string s1, int start, int end)
{
    char *t = malloc((end - start) * sizeof(char));

    for (int j = 0; j < end - start; j++)
    {
        t[j] = s1[j + start];
    }
    
    return t;
}

/**
 * gives next word based on incrementLetter
 * getNextWord("abc") => "bbc"
 */
string getNextWord(string s1)
{
    char first_letter = s1[0];
    if (first_letter == ' ')
    {
        s1[0] = 'A';
    }
    else if (first_letter == 'Z')
    {
        s1[0] = 'a';
    }
    else if (first_letter < 'z')
    {
        s1[0] = incrementLetter(first_letter);
    }
    else if (first_letter == 'z')
    {
        string first_letter_str = slice(s1, 0, 1);
        first_letter_str[0] = 'A';
        string next_word_substr = slice(s1, 1, strlen(s1));
        if (!next_word_substr[0])
        {
            next_word_substr[0] = 'A';
        }
        else
        {
            next_word_substr = getNextWord(next_word_substr);
        }
        
        return ARRAY_CONCAT(char, first_letter_str, 1, next_word_substr, strlen(next_word_substr));
    }
    
    return s1;
}

/**
 * compares 2 strings
 * equals("abc", "abc") => true
 * equals("abc", "bcd") => false
 */
bool equals(string s1, string s2)
{
    if (strlen(s1) != strlen(s2))
    {
        return false;
    }
    for (int i = 0; i < strlen(s1); i++)
    {
        if (s1[i] != s2[i])
        {
            return false;
        }
    }
    return true;
}

int main(int argc, string argv[])
{
    if (argc != 2)
    {
        printf("Usage: ./crack hash\n");
        return 1;
    }
    
    hash = argv[1];
    char *word = malloc(6 * sizeof(char));
    string salt = slice(hash, 0, 2);
    word[0] = ' '; // special char to start populating word
    while (!success)
    {
        word = getNextWord(word);
        success = equals(crypt(word, salt), hash);
    }
    printf("word: %s\n", word);
}